Optical filters are exceptionally useful devices for processing light signals, and have found numerous applications in fiber optic communication systems for separating different wavelengths of light which can carry different communications signals. A number of other applications use optical filters for selectively reflecting or transmitting a light signal, and can thus be employed to re-direct an optical signal within an optical switch, wavelength division multiplexer, or other light processing equipment.
Optical filters are typically constructed from thin films of optical materials with varying indices of refraction, thus forming a multilayer assembly. One characteristic of thin film optical filters is that their transmission (and reflection) characteristics are dependent on the angle at which the light strikes the filter. Because of this angular dependency, a thin film optical filter must be aligned properly in order to provide the desired wavelength or polarization filtering function. Rotating an optical filter about an axis which is perpendicular to the incident light provides a means of tuning the filter and can be used to obtain the desired optical response of the system.
In any optical system where an optical filter is rotated to tune the filter, it is important to have an adequate means for rotating and securing the filter. Motorized stages can be utilized to tune a filter, but are expensive and not suited for small high-volume optical components. Other mechanical rotating stages may be suitable for laboratory work, but as with motorized stages, are not suitable for small high-volume components. Additionally, it is necessary to have the ability to mount and rotate several filters to produce a wavelength division multiplexer with multiple outputs.
For the foregoing reasons, there is a need for an apparatus for holding and tuning a thin film optical assembly.